Redirects you to the proper URL of the website. In case of stumbling upon a working alias.
Normally (depending on your settings or control panel) http://misterwebsite.nl (an alias of www.mrwebsite.nl) just works, but it should be redirected to http://www.mrwebsite.nl.
The same goes for http://mrwebsite.nl (it should be with www. instead without), https://www.mrwebsite.nl (it should be http instead of https) and all other aliases.
Before WordPress 3 this just worked out of the box. But it does not anymore.